The MegaCommand is an open-source MIDI controller that runs the MCL firmware for use with the Elektron Machinedrum. It is is based around the Arduino Mega 2560.
The printed cicuit board is a through-hole design (no SMD soldering skills required).
- 4 x MIDI ports (2 in, 2 out)
- 4 x Rotary Encoders + Push button
- 4 x Buttons
- 1 x OLED display
- SD Card
- 128KBytes of SRAM (0-63KB accessible natively, 64-128KB accessible with bank selection)
- 2 x 10pin Expansion ports
Stack is 8KB in size. 56KB of SRAM reserved for global objects, variables. (bank switchable)
The MCL respository contains the software component of this project. https://github.com/jmamma/MCL
Board revision: 1_0_2a12
ALL INFORMATION BELOW IS PROVIDED AS A CONVENIENCE AND COULD BE SUBJECT TO ERROR OR CHANGE.
1.0.2a: https://github.com/jmamma/MegaCommand_Design/blob/master/1_0_2/bill_of_materials
OLED 128x32, it uses the SPI bus.
Important: OLED display requires resistor position changes to enable SPI mode as per adafruit documentation https://learn.adafruit.com/2-3-monochrome-128x32-oled-display-module/assembly-1):
You can easily get your own PCBs made.
PCBWay.com fabrication options
Gerber files (pcb layout diagrams used for fabrication) are included in the ./gerber/ directory above.
Download gerbers and submit to PCB manufacturer.
Circuit Schematic and Board Layout is present in Eagle files.
1.0.2a:
The enclosure can be 3D printed. The design files and variations are located in:
https://github.com/jmamma/MegaCommand_Design/tree/master/Enclosure/OLED/3D
Optionally print 4 spacers and superglue to the screw holes on the OLED to ease installation of the screen at the proper height.
The build is organised in to multiple stages. You must follow the order sequentially. At the end of each stage there is a test checkpoint. It is important that you perform these tests to ensure each stage is working before proceeding to the next, failing to do so will make troubleshooting any problems much harder.
VERIFY CHIP ORIENTATION BEFORE SOLDERING.
OLED display must be installed last.
Take care in making sure the ICs are inserted the correct way around.
## Build Order:
1. ICS: RAM, Octal Latch, Shift Registers
2. Arduino male headers.
3. Capacitors. (Make sure the 220uF electrolytic cap fits when the arduino is connected)
(10uF +ve terminal is soldered to pad closest to SD card holder.
TEST POINT: Run the SRAM firmware test.
4. MEC switches (Make sure these sit completely flush with the board and are not leaning to one side)
5. Resistor arrays
6. Encoders (Make sure these sit completely flush with the board and are not leaning to one side)
TEST POINT: Run the button and encoder test firmware.
7. ICS: MIDI Optocouplers.
8. Resistors + diodes
9. MIDI DIN ports.
TEST POINT: Insert SD Card, Run the MIDIPort test firmware.
10. Power Jack (+9V tip)
11. Yamaichi SD card holder.
TEST POINT: Run the SDCARD test firmware
OLED Display:
12. Oled display requires correct resistor poisiton in order to be configured for SPI mode. (See documentation above to confirm the resistor placement)
13. Male header to be soldered to OLED board. Header is then soldered on to MegaCommand PCB. The height of the OLED display is important. The distance between the mainboard pcb, and the bottom on the OLED pcb should be 5mm when soldered.
14. LEDs (+ anode pin nearest to the bottom of the board for both LEDs. ). When soldered, the tip of the LED should measure 11mm above mainboard pcb.
15. Power switch. (optional, you can solder a short between the two right most pins on EG1212B
Expansion Headers:
16. These are short 5mm headers. It might not be possible to buy them at the right length so you'll need to cut them down to 10 pin.
TEST POINT: Run the LCD and LED test firmware.
## Important
OLED Display must be installed last.
5) To install the male headers that connect to the MegaCommand to the ArduinoMega, insert the headers in to the ArduinoMega then solder with the arduino attached to the headers. This will ensure perfect alignment.
Once you've built a MegaCommand you can upload the latest version of the MCL firmware located here: https://github.com/jmamma/MCL/releases
If you're familiar with coding you can write sketches within the Arduino IDE to test the hardware and run custom firmwware. Before you start coding you need to decide which core you are going to use.
In ArduinoIDE, a Core is a collection of initialisation functions and associated libraries, used for configuring the underlying hardware; it is analogous to an Operating System kernel.
The cores availabile in the Arduino IDE are listed under Tools -> Boards.
Arduino Mega or Mega 2560:
This is the standard core that comes installed default with the Arduino IDE. If you use this core with the MegaCommand you can program the MegaCommand like an ordinary arduino shield. The built in arduino functions can be used to control the hardware using the pin assignement detailed below.
MCL Core:
This was built on top of Manuel Odendahl's core for the MiniCommand. By using this core you can take advantage of the powerful MIDI libraries and GUI functionality.
For example, the MegaCommand core is necessary for running the MCL firmware, and controlling the Elektron instrument range.
(Instructions for OSX, should be similar for Windows)
-
Download the Arduino IDE https://www.arduino.cc/en/Main/Software (1.8.5 tested)
-
Get the MIDICtrl library and MegaCommand Core (same repo):
cd /Applications/Arduino.app/Contents/Java/hardware/
git clone https://github.com/jmamma/MCL
- Open the Arduino IDE, Under the Tools menu, select the core you wish to use from the "Board:" menu
The default Arduino core is named "Arduino/Genuino Mega or Mega 2560"
The MegaCommand core will be listed at the bottom.
The MegaCommand shield was designed to be backwards compatible with the original MiniCommand hardware.
However, there are notable differences between the two systems, including new pin assignments which must be taken account for when using the original MidiCtrl libraries.
The original MiniCommand used the ATMega64 microprocessor whilst the MegaCommand Shield is built on top of ArduinoMega which uses the ATMega2560 processor. The ATMega2560 shares most of the IO functionality of the ATMega64 but has additional pins, and a different pin-to-port layout.
The MegaCommand Shield accesses the ATMega2560 processor on board the ArduinoMega through the exposed headers, not all pins on the ATMega2560 are exposed through this Arduino interface.
Incorporating the differences between both processors and subsequent pin availability the following pin assignment has been made as the best possible substitutes for the original hardware layout.
4 Midi Ports vs 3
256k ROM vs 64K
USB vs No USB
--
MegaCommand pin changes from original MiniCommand are as followed:
MicroSD board:
CS = PB0
SRAM
BankSel = PL6
Key Scanning (Shift Register Circuit):
PL0 = OUT
PL1 = SHIFT
PL2 = CLK
HD44780 LCD Circuit:
E = PL4
R/S = PL3
LEDs:
PE5 = LED0
PE4 = LED1
MIDI:
TXD0 and RXD0 (USART0) are reserved for Arduino USB interface.
Therefore we shift midi ports by 1.
MIDI Port 1:
RXD1 = MIDI Port 1 IN.
TXD1 = MIDI Port 1 OUT
Midi Port 2:
RXD2 = MIDI Port 2 IN
TXD2 = MIDI Port 2 OUT ( New port, not available on original Minicommand)